Causes of endocarditis

Your heart is usually well protected against infection, and bacteria usually pass harmlessly by.

However, if your heart valves are damaged or if you have an artificial valve, it will be easier for bacteria to take root and bypass your normal immune response to infection.

The bacteria multiply and spread across the inner lining of your heart (the endocardium). The endocardium becomes inflamed, causing damage to your heart valves.

Once damaged, the valves may no longer be able to supply your heart with the blood it needs, leading to heart failure.

Small clumps of bacteria can develop in the heart at the site of the infection. There is a risk that these clumps will act in a similar way to blood clots, travelling away from the heart and blocking the blood supply to the organs, which can cause organ failure or trigger a stroke.

How bacteria reach the heart

The most common ways that bacteria can enter your blood are explained below.

Mouth

Everyday activities, such as brushing your teeth or chewing your food, can sometimes allow bacteria to enter the bloodstream. The risk is increased if your teeth and gums are in bad condition, because it makes it easier for bacteria to enter.

Infection

Bacteria can spread from the site of a pre-existing infection, such as a skin infection or a gum infection.

Prosthetic valves

However, bacteria can also take root around prosthetic valves, which can occasionally trigger endocarditis. This risk is relatively low, estimated to be less than one in 100.

Intravenous drug use

People who habitually inject illegal drugs such as heroin or methamphetamine (crystal meth) into their veins have an increased risk of developing endocarditis. This is because of unsterilised needles allowing bacteria to enter the bloodstream and repeated injections making the skin more vulnerable to infection.

Fungal endocarditis

Endocarditis caused by a fungal infection is rarer than bacterial endocarditis, and usually more serious. You are more at risk of fungal endocarditis if you:

inject drugs

have a history of heart surgery

have a central venous catheter (a tube that is connected to a vein in the neck, groin or chest, and is used to deliver medicines and/or fluids to people who are seriously ill)

have a weakened immune system, either as a result of a condition affecting the immune system, such as HIV, or as a side effect of certain types of treatments, such as chemotherapy